Measuring machine

ABSTRACT

An analogue measuring machine has a sensing mechanism which reacts against a resistance mechanism, measurement being indicated by an indication mechanism driven by the sensing means. The indication mechanism comprises a thin flexible band which extends between first and second pulley wheels and has its ends secured to the pulley wheels. The first pulley wheel is driven by the sensing means to move an index carried by the band relatively to a scale. A driving means is arranged so that the second pulley wheel is driven in unison with the first pulley wheel to maintain the length of the band between the first and second pulley wheels constant.

United States Patent 1191 Perry 1 Feb. 27, 1973 [54] MEASURING MACHINE [22] Filed: Nov. 2, 1970 [21] Appl. No.: 85,974

[30] Foreign Application Priority Data Nov. 6, 1969 Great Britain ..54, 374/69 [52] U.S.Cl. ..ll6/114,1l6/135,l77/246 [51] 1nt.Cl. ..G0ld2l/00 [58] Field of Search....ll6/l16, 135, 124.1, 124.1 A, 1l6/124.1R,l14,124;185/9,l0,14, 44; 177/234, 230, 175, 246, 229, 225, 17'

2,844,039 7/1958 Spakman ..74/l0.7

FOREIGN PATENTS OR APPLlCATlONS 437,237 10/1935 Great Britain ..l16/124.1 A

893,500 1/1944 France ..l l6/DlG. 6

Primary Examiner-Louis J. Capozi Attorney-Mawhinney & Mawhinney [57] ABSTRACT An analogue measuring machine has a sensing mechanism which reacts against a resistance mechanism, measurement being indicated by an indication mechanism driven by the sensing means. The indication mechanism comprises a thin flexible band which extends between first and second pulley wheels and has its ends secured to the pulley wheels. The first pulley wheel is driven by the sensing means to move an index carried by the band relatively to a scale. A driving means is arranged so that the second pulley wheel is driven in unison with the first pulley wheel to maintain the length of the band between the first and second pulley wheels constant.

14 Claims, 19 Drawing Figures SHEET-10F e PATENTEDIFEBZTISHV INVENTOR DAVID LESTER EDGAR PEQQY PATENTEDFEBZYIQB 3,71 ,112

' sax-112w 6 INVENTOR DAV b LESTER EbaAa 222 :PmEmiuw im 4 3718.112

. SHEET 3'UF6- INVENTOR DAvu LESTER EbGAR ezmr PATENTEDFEBZ? 1915 SHEET 5 OF 6 TOR DGAR P z IN DAvu L; 51-52 MEASURING MACHINE The invention concerns improvements in or relating to an analogue measuring machine and is particularly, but not exclusively, concerned with a weighing machine. I

In a measuring machine it is necessary to provide a sensing means which will react dependent on the property to be measured, and an indication mechanism which will interpret the reaction of the sensing means into an intelligible indication of the value of the property. In a weighing machine, for example, the weight of an article may be applied through'a sensing means in the form of a resistance mechanism incorporating a metering spring, and the movement of the resistance mechanism may be used to drive an indication mechanism such as a pointer moving over a scale. For such a weighing machine to give accurate results, it is necessary either for the indication mechanism to require substantially no driving force, or for the scale to be calibrated to correct for the driving force required to operate the indication mechanism. The latter of these solutions is not satisfactory if the measuring machine is to have a linear scale, and a common solution is to arrange for the indication mechanism to be a balanced pointer supported in substantially frictionless bearings however, this necessitates the use of radial calibrations if a linear relationship is to be preserved. Although such radially calibrated linear scales are commonly used, they are inherently costly to manufacture when compared with a parallely calibrated linear scale. I An index can be supported by an endless filament passing over a first pulley wheel driven by the sensing mechanism and over an idler pulley wheel, but this arrangement is unsatisfactory in that the filament is liable to slip if the driven pulley wheel is suddenly moved thereby causing loss of calibration, and it is very difficult to support an index from the filament due to the tendency for the filament to twist under the weight of the index. To prevent the danger of the filament slipping, the filament can be secured at one point to the driven pulley wheel however this solution creates an additional problem as the useful travel of the filament is then a fixed function of the circumference of the driving pulley wheel and it becomes necessary to make at least the driving pulley wheel of an inordinately large diameter. In fact, if the driving and idler pulley wheels are of the same diameter, the overall length of the scale must be multiplied by a factor of at least 1.64 to give the length of casing required to accommodate the mechanism. In this event the scale can only occupy up to 61 percent of the length of the casing. Furthermore, if the filament includes a self-tensioning element, the casing may have to be as much as twice th e length of the scale. An object of the present invention is to provide an improved indication mechanism for moving an index over a scale with parallel calibrations.

According to the invention an indication mechanism, for moving an index relatively to a scale with parallel calibrations, includes first and second pulley wheels supported for rotation by substantially frictionless bearings about parallely spaced axes of rotation, a thin flexible band having its ends respectively secured to the pulley wheels, a portion of the band extending between the two pulley wheels being arranged to move the index relatively to the scale, the first pulley wheel being arranged to be driven by the sensing means of an analogue measuring machine to move the band and thus to move the index relatively to the scale, the second pulley wheel being driven to maintain the length of said portion of the band constant, and the band in one position being wound at least one full turn on one of the two pulley wheels. Preferably the band bears the index for movement along the scale which is arranged parallely adjacent said portion of the band. Alternatively, the scale may be carried by the band, the index being arranged adjacent the scale. In the event that the band can be unwound one full turn from said one pulley wheel without moving the index off the scale, the scale can occupy up to 76 percent of the easing length. Preferably the band in one position is wound a plurality of turns on said one pulley wheel. In the event that the band can be unwound two full turns from said one pulley wheel without moving the index off the scale, the scale could occupy up to 86 percent of the casing length, and if three full turns are possible the percentage increases to 90 percent. The band may be in the form of a constant force spring tape preset throughout its operative length to the same curvature whereby the unwinding of the band from either of the pulley wheels will cause a corresponding rotation of the other pulley wheel to maintain the length of said portion of the band constant. The invention to this point enables an index to be moved relatively to a parallely calibrated scale whilst enabling the size of the pulley wheels to be kept to a reasonable diameter and the scale to be of a sensible length. However, unless the band is in the form of a constant force spring tape, it will be necessary to provide a mechanism for driving the second pulley to maintain the tension in the band whilst it is unwinding from the first pulley wheel, and the applicability of the indication mechanism will de.- pend on the strain energy stored in the portions of the band coiled on the pulley wheels and whether this strain energy is either balanced to cause a null efiect, or is so small as to be negligible, or is deliberately exploited as a resistance mechanism.

Preferably the second pulley wheel is driven to maintain the tension in the band whilst it is unwinding from the first pulley wheel by a mechanism including third and fourth pulley wheels supported for substantially frictionless rotation respectively about the axes of rotation of the said first and second pulley wheels, a second thin flexible band having its ends respectively secured to the third and fourth pulley wheels, the third and fourth pulley wheels being drivingly connected respectively to the first and second pulley wheels for joint rotation, said second band being arranged so that rotation of the first pulley wheel in a sense to unwind the first band will result in an equivalent length of the second band being wound onto the third pulley wheel thereby causing the fourth pulley wheel to drive the second pulley wheel in a sense to wind up a length of the first band equal to the length unwound from the first pulley wheel, the length of the second band and the number of windings about the third and fourth pulley wheels being adequate to permit full movement .of the index over the scale. According to one feature, the first band may be wound around the first and second pulley wheels in opposite senses taken from its ends. Thus, if the first band is wound clockwise from one end about the first pulley wheel and counterclockwise from the other end about the second pulley wheel, the second band will be wound counterclockwise from one end about the third pulley wheel and clockwise from the other end about the fourth pulley wheel. In this case, the first and second bands may be made of a material and of such a thickness that the strain energy in the wound portions of the tapes is negligible when compared with the operating forces generated by the sensing means of the measuring machine. Altematively, the first and second bands may be made of a material and of such a thickness that the strain energy in the wound portions of the tapes is sufficient to constitute a resistance mechanism for the sensing means of the measuring machine. I

Preferably the first band is wound around the first and second pulley wheels in the same sense taken from its ends, and the first and second bands are arranged so that the strain energy applied at any position to the first pulley wheel is substantially equal to the strain energy applied at the same position to the fourth pulley wheel, and the strain energy applied at any position to the second pulley wheel is substantially equal to the strain energy applied at the same position to the third pulley wheel.

The first and second bands may be tensioned by means of a torsional tensioning device reacting between either the first and third or the second and fourth pulley wheels.

Desirably the second band also bears an index or scale for movement along a scale or index arranged parallely adjacent the portion of the band extending between the third and fourth pulley wheels. The first band together with its associated index and scale may be arranged to be viewable from one position, and the second band together with its associated index and scale lies in a plane spaced parallely away from the first band to be viewable from another position. This enables an analogue measuring machine, for instance a weighing machine used in a shop, to provide separate displays of weight and price to both the customer and the shop assistant. In the case where the first band is wound around the first and second pulley wheels in the same sense taken from its ends, one or more additional pulley wheels may be employed to engage one or both of the bands to maintain the bands substantially parallel to each other.

In an alternative arrangement the second pulley wheel is driven to maintain the tension in the band whilst it is unwinding from the first pulley-wheel by a mechanism which is driven by the sensing means of the analogue measuring machine in unison with the first pulley wheel.

At least one end of the band (or one of the bands as the case may be) is preferably secured to its corresponding pulley wheel by means of a fixing device lying within the periphery of the pulley wheel, the band being led to the fixing device through a curved slot or passage formed in the pulley wheel and having a smoothly curved juncture with the cylindrical operative surface of the pulley. Desirably, the curved slot or passage is a transition curve from the cylindrical operative surface of the pulley.

A member having a cylindrical outer surface may be mounted for rotation about its axis which is parallely spaced from the portion of the band extending between its two pulley wheels, and the cylindrical member defines the scale and a number of other scales which can be moved into position by rotating the cylindrical drum. The band is preferably formed at least partly of translucent material and the index is an opaque mark on the band. Alternatively the band may be formed from a translucent portion and an opaque portion, the juncture serving as the index.

According to another aspect of the invention, an analogue measuring machine has its sensing means arranged to drive an indication mechanism of the kind disclosed. In the eventthat the machine is a weighing machine, the sensing means may include a lever pivotally mounted at one end for swinging movement against a resistance mechanism, the lever remote from its pivotal axis being provided with a segmental rack which drives a gear fast with the first pulley wheel, and the center of curvature of the segmental rack being coincident with the pivotal axis of the lever.

The invention is now described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic side elevation of one embodiment of the invention;

FIG. 2 is a plan view of FIG. 1;

FIG. 3 is a perspective diagram illustrating the operation of the embodiment shown in FIGS. 1 and 2;

FIG. 4 is a diagrammatic side elevation of a preferred embodiment of the invention;

FIG. 5 is a plan view of FIG. 4;

FIG. 6 is a perspective diagram illustrating the operation of the embodiment shown in FIGS. 4 and 5;

FIG. 7 is a side elevation of an analogue weighing machine incorporating the indication mechanism illustrated in FIGS. 4 to 6;

FIG. 8 is a plan view of FIG. 7;

FIG. 9 is an end view of FIG. 7 taken in the direction of arrow 9;

FIG. 10 is a perspective diagram illustrating the interrelation of the operating parts of the weighing machine illustrated in FIGS. 7 to 9;

FIG. 11 is a detail of one of the rollers, shown partly in section, and illustrating the preferred manner of securing the ends of the bands to the rollers;

FIG. 12 is an end elevation of FIG. 11 taken in a direction of arrow 12;

FIGS. 13, 14 and 15 illustrate minor modifications of the embodiment disclosed in FIGS. 4 to 10 to enable a dual reading to be obtained conveniently;

FIGS. 16 and 17 are diagrammatic side elevations of alternative embodiments of the invention;

FIG. 18 illustrates an application of the embodiment shown in FIG. 17, and

FIG. 19 is a diagrammatic side elevation of another alternative embodiment of the invention.

With reference to the embodiment shown in FIGS. 1 to 3, an indication mechanism, for moving an index 20 along a scale 21 provided with parallel calibrations, includes first and second pulley wheels 22 and 23 sup ported by respective shafts 24 and 25 which are arranged parallel to each other and are supported for rotation by unshown substantially frictionless bearings from an unshown rigid casing.

The first and second pulley wheels 22 and 23 are interconnected by means of a thin flexible band 26 having its ends secured to the pulley wheels 22 and 23 by respective fixings 27 and 28 which will later be described in detail with reference to FIGS. 11 and 12. From the fixing 27, the band 26 is wrapped in a clockwise sense three times around the pulley wheel 22 and extends parallely adjacent the scale 21 to the second pulley wheel 23 around which it is wrapped one and one-half revolutions in the counter-clockwise sense from the fixing 28. As will later be described by way of example with reference to FIGS. 7 to 10, the first pulley wheel 22 is conveniently driven by the sensing means of an analogue weighing machine through a gear wheel secured to the shaft 24, and it will be appreciated that rotation of the first gear wheel 22 in a counterclockwise sense will move the index to the left along the scale 21. However, movement of the first pulley wheel 22 in the clockwise sense would tend to allow the band 26 to go slack and it is accordingly necessary to provide some form of drive to the second pulley wheel 23 to enable the tension in the band 26 to be maintained. This is conveniently achieved by means of third and fourth pulley wheels 29 and 30 made drivingly fast respectively with the first and second pulley wheels 22 and 23 through the respective shafts 24 and 25. A second band 31 has its ends secured to the third and fourth pulley wheels 29 and 30 by means of respective fixings 32 and 33. From the fixing 32, the band 31 is wrapped one and one-half times around the third pulley wheel 29 in a counterclockwise sense and then extends in a taut condition to the fourth pulley wheel 30 around which it is wrapped three complete revolutions in the clockwise sense from the fixing 33. In this manner, clockwise rotation of the first pulley wheel 22 will cause the third pulley wheel 29 to wind in the band 31 thereby causing a corresponding clockwise movement of the fourth pulley wheel 30 and the second pulley wheel 23. The latter is able to wind in the band 26 at the same rate that it is wound 011 the first pulley wheel 22, thereby preventing it from going slack.

Provided that the first and second bands are made of a material and of such a thickness that the strain energy in the wound portion of the bands 26 and 31 is negligible compared with the operating force generated by the sensing means, the mechanism showing FIGS. 1 to 3 will operate satisfactorily as an indication mechanism. However, it will be appreciated that strain energy will exist in the portions of the bands wound onto the four pulley wheels 22, 23, 29 and 30, and that the strain energy will vary according to the number of turns of the bands 26 and 31. For convenience, the magnitude of the strain energy will be expressed as symbol T." Although the total strain energy on each pair of pulley wheels 22 and 23, and 29 and 30 will remain constant, the balance will change as indicated in FIG. 3 where it will be noted that a strain energy of T is trying to rotate the pulley wheels 22 and 30 in the clockwise sense, whereas the strain energy of T is trying to rotate the pulley wheels 23 and 29 in the counterclockwise sense;

T being of greater magnitude than T As a result, both of the shafts 24 and have a torsional resultant of (T T applied in the clockwise sense which would tend torestore the index 20 to the center of the scale 21. Thus, the displacement of the index 20 in either direction from the null position (in which an equal amount of band is wound on each pulley and T, T will result in a progressively increasing restoring force of 2(T T depending on the number of turns of the bands 26 and 31 on the pulleys 22, 23, 29 and 30. In other words movement of the index 20 from the center of the scale 21 will meet an increasing resistance force, and the mechanism can accordingly also be used as a resistance mechanism for the measuring machine. Although this mechanism conveniently provides a bidirectional efiect by arranging the index 20 to move in either direction from a null or zero point at the center of the scale 21, the index 20 could be moved to a different position on the band 26 so that all measuring movement occurs in the same direction thereby resulting in a uni-directional mechanism. However, it should be noted that the restoring force of 2(T, T increases progressively so that displacement of the index 20 will not be linear. Thus. this mechanism, would nppear to be most acceptable in its bi-directional form as a light-or-heavy" indicator for checkweighing of produce to be packaged in predetermined weights. If it is desired to use the mechanism additionally as a resistance mechanism, the bands 26 and 31 could be made as thin strips of spring steel, but on the other hand, if the strain energy effect is to be'reduced to a minimum to enable the mechanism to be used purely as an indication mechanism, the bands 26 and 31 could be made out of very thin section plastic tape.

In the event that .it is desired to eliminate completely the effect of strain energy in the bands, the embodiment now described with reference to FIGS. 4m 6' can be arranged appropriately. As will be noted from' FIG. 6, the torsional resultant on each of the shafts .24 and 25 can again be expressed as (T, T but these resultants are in opposite senses and cancel out for all values of strain energy T. This arrangement is shown in the weighing machine now described with reference to FIGS. 7 to 10, in which a base 40 is provided with in.- tegral pairs of pillars 41 and 42 which respectively support bearings 43 and 44 for the shafts 24 and 25. The Y indication mechanism described with reference to FIGS. 4 to 6 has been employed and the same reference numerals have been utilized to indicate equivalent components. It will be noted that the band 31 has been utilized to move the index 20 along the scale which is in the form of a cylinder 45 mounted for rotation from brackets 46 secured to the front pillars 41 and 42. In

this manner, the cylinder 45 is able to rotate about an axis parallely spaced from the band 31, and an operating knob 47 is provided, as shown in FIG. 10, for indexing the cylinder 45 to different positions. Thus, the cylinder 45 can be calibrated with a number of price scales and the index 20 can be used to compute the cost of the goods weighed, the operating knob 47 being utilized to index the cylinder 45 to present the appropriate scale.

The pulley wheels 22 and 29 are driven by a common spur gear 48 which is operated by a segmental rack 49 connected by a compensating pivot 50 to the end of the balance lever 51. A resistance mechanism, in the form of a tension coil spring 52 is suspended from a bridge 53 connected across the top of the pillars 41 and carries a stirrup 54 at its bottom end. The lever 51 is provided with a cross member 55 supporting a knife-edge 56 which reacts in the stirrup 54, the opposite end of the balance lever 51 being supported from the pillars 42 by a transverse pivot 57. To ensure accuracy, the center of the segmental rack 49 should be coincident with the axis of the pivot 57. The weighing pan would be secured to the top of a pedestal 58 which is connected to a saddle 59 pivoted about an axis 60 to the balance lever 51. In order to ensure that the pedestal 58 stays vertically above the saddle 59, its motion is controlled by a link comprising a spring steel leaf 61 which is secured at one end to the pedestal 58, and at the other end to a bridge 62 across the top of the pedestals 42. In order to prevent the spring leaf 61 from buckling, a pair of rigid plates 63 .are secured to its upper and lower faces for the majority of its length as shown in FIG. 7.

If desired, both of the bands 26 and 31 may be utilized to move respective indexes over separate scales thereby providing a dual read-out capability. Under these circumstances, the mechanism shown in FIGS. 1 to 3 could conveniently be used as the bands 26 and 31 are parallel to each other. However, the difficulty does occur with the arrangement shown in FIGS. 4 to 6 in that the bands 26 and 31 are no longer parallel to each other and it may be undesirable for one of thescales to be other than horizontal or perhaps vertical as the case may be. To avoid this problem, the mechanism shown inFIGS. 4 to 6 canbe modified as shown in FIGS. 13, 14 or whereby rollers 70 are used to control either one or both of the bands to achieve a condition in which the reading portions of both bands are parallel.

Although the index could be a separate pointer carried by one or both of the bands 26 and 31 as indicated in FIGS. 1 to 6, it could merely be a mark on a translucent band as indicated in FIGS. 8 and 10. Furthermore, the index could be provided as the juncture between an opaque ribbon and a transparent ribbon joined together to form one of the bands 26 or 31. If desired, the spur gear 48 and segmental rack 49 can be replaced by any convenient mechanism for transmitting movement of the balance lever 51 into corresponding rotational movement of the pulley wheels 22 and 29. I

It will be appreciated that it is most important for the bands 26 and 31 to be secured to their respective pulley wheels 22, 23, 29 and 30 in such a manner that the multiple turns of the bands cause minimal interference to the rotation of the pulley wheels. Such an arrangement is illustrated in FIGS. 11 and 12 from which itwill be noted that a pulley wheel 22 is provided with a peripheral track 71 for accommodating the turns of the band. From the peripheral tracks 71 a slot 73 is cut as a transition curve, and terminates in a cylindrical pocket 74 parallely spaced from the axis of the shaft 24. A spool 75 is arranged for rotation in the cylindrical pocket 74 and has ahead 76 provided with a dia'metral cut 77 for engagement by a screwdriver for adjustment purposes. The spool has a bifurcated body 78 through which the band is threaded and the length of the band is adjusted simply by rotating the spool 75 until the desired length is obtained. A locking screw 79 is provided to clamp the periphery of the head 76 after the band has been adjusted to the desired condition.

After the lengths of the bands have been adjusted appropriately, it may be desired for them to be tensioned and this can be achieved conveniently by arranging for a tensioning device to be arranged either between the pulley wheels 22 and 29, or the pulley wheels 23 and 30 to cause a slight relative rotation thereby tensioning the whole system. Alternatively, one of the shafts 24 or 25 could be mounted from a carriage in a slide lying in the general direction of the bands 26 and 31, the carriage being tensioned by a spring in the desired direction.

As shown in FIG. 16, the tension in the band 26 can be maintained by passing the band 26 over a tensioning pulley 80 supported by an axle 81 from unshown substantially frictionless bearings carried in a tensioning slide operated by a spring with a force of (T, T The band 26 is operable in both directions by gearing the pulleys 22 and 23 together by means of respective coaxial gears 82 and 83. This arrangement is operationally similar to that shown in FIGS. 1 to 3 as there is an inherent restoring force of (T T towards the zero or null position.

FIG. 17 illustrates an alternative arrangement to FIG. 16 in which the tensioning pulley 81 is omitted and the gears 82 and 83 are interconnected by a rack 84. If desired the rack 84 could be replaced by any suitable mechanical equivalent.

FIG. 18 illustrates an application of the arrangement shown in FIG. 17 to a weighing machine, in which the weighing pan 85 drives the rack 84 against a metering spring 86, the band 26 having indices 20 moving over scales 87 and 88.

In the embodiments shown in FIGS. 13 to 18 care must be taken to ensure that frictional forces are kept to an acceptable minimum.

FIG. 19 illustrates an alternative arrangement .to FIGS. 16 and 17 in which the tension in the band 26 is maintained by forming the band 26 from a length of constant force spring tape. This material is already known per se from its application in constant force spring motors. The spring tape is preset throughout its length to the same curvature. With this characteristic the spring tape has the property that the application of thetwo opposite and equal forces T in FIG. -19 will maintain the portion of the spring tape 26 extending between the pulleys 22 and 23 straight at all times without the application of any additional external forces. Because the forces T act radially with respect to the shafts 24 and 25 no restoring force is applied to bias the spring tape 26 into any specific position between the pulleys 22 and 23.

What I claim as my invention and desire to secure by Letters Patent of the United States is:-

1. An indication mechanism, for moving an index relatively to a scale with parallel calibrations responsive to the sensing means of an analogue measuring machine, comprising first and second pulley wheels substantially frictionless bearings supporting said first and second pulley wheels for rotation about parallely spaced axes of rotation, a thin flexible band has its ends respectively secured to said first and second pulley wheels, a portion of said band positioned between said first and second pulley wheels and connected to the index to move said index relatively to said scale, said first pulley wheel being driven by said sensing means of the analogue measuring machine to move said band and thereby to move said index relatively to said scale, driving means for driving said second pulley wheel to maintain the length of said portion of the band con stant, and said band in one position being wound at least one full turn on one of said pulley wheels.

2. An indication mechanism, as in claim 1, in which said thin flexible band is in the form of a constant force spring tape preset throughout its operative length to the same curvature, said band thereby constituting said driving means whereby the unwinding of said band from either of said pulley wheels will cause a corresponding rotation of the other of said pulley wheels to maintain the length of said portion of the band constant.

3. An indication mechanism, as in claim 1, in which said driving means is a mechanism including third and fourth pulley wheels and substantially frictionless bearings supporting said third and fourth pulley wheels for rotation respectively about the said axes of rotation of the said first and second pulley wheels, a second thin flexible band has its ends respectively secured to said third and fourth pulley wheels, said third and fourth pulley wheels are connected respectively to said first and second pulley wheels for joint rotation, said second band being arranged whereby rotation of said first pulwound onto said third pulley wheel thereby to cause said fourth pulley wheel to drive said second pulley wheel in the sense to wind up a length of said first band equal to the length unwound from said first pulley wheel, the length of said second band and the number of windings of said'second band about said third and fourth pulley wheels being adequate to permit full movement of the index over the scale.

4. An indication mechanism, as in claim 3, in which said first band is wound around said first and second pulley wheels in opposite senses taken from the ends of said first band.

5. An indication mechanism, as in claim 3, in which said first band is wound around said first and second pulley wheels in the same sense taken from the ends of said first band whereby the strain energy applied by said first band to said first pulley wheel in any position of said mechanism is substantially equal to the strain energy applied by said second band to said fourth pulley wheel in the same position of said mechanism, and the strain energy applied by said first band to said second pulley wheel in any position of said mechanism is substantially equal to the strain energy applied by. said second band to said third pulley wheel in the same position of said mechanism.

6. An indication mechanism, as in claim 3 in which a second index is connected to said second band for movement along a second scale arranged parallely adjacent the portion of said second band extending between said third and fourth pulley wheels.

7. An indication mechanism, as in claim 3, in which said-first band is wound around said first and second pulley wheels in the same sense taken from the ends of said first band whereby the strain energy applied by said first band to said first pulley wheel in any position of said mechanism is substantially equal to the strain energy applied by said second band to said fourth pulley wheel in the same position of said mechanism and the strain energy applied by said first band to said second pulley wheel in any position of said mechanism is substantially equal to the strain energy applied by said second band to said third pulley wheel in the same position of the mechanism, a second index is connected to said second band for movement along a second scale arranged parallely adjacent the portion of said second band extending between said third and fourth pulley wheels, and at least one additional pulley wheel is positioned to engage one of said bands to hold said one band substantially parallel to the other of said bands.

8. An indication mechanism, as in claim 1, in which said driving means is a mechanism driven by said sensing means of the analogue measuring machine and said mechanism is connected to drive said second pulley wheel in unison with the first pulley wheel to maintain the tension in said band whilst it is being unwound from said first pulley wheel.

9. An indication mechanism, as in claim 1, in which at least one end of said band is secured to its aforesaid corresponding pulley wheel by means of a fixing device positioned within the periphery of said corresponding pulley wheel, said corresponding pulley wheel defining a curved passage having a smoothly curved juncture with the cylindrical operative surface of the pulley wheel, and said band being led to said fixing device through said curved passage.

10. An indication mechanism, as in claim 1, in which a member having a cylindrical outer surface is mounted for rotation about its axis which is parallely spaced from said portion of said band extending between said first and second pulley wheels, and said cylindrical member defines said scale and a number of other scales which can be moved optionally into operative position adjacent said index by rotating said cylindrical drum.

11. An indication mechanism, as in claim 10, in which said band is formed at least partly of translucent material, said index is an opaque mark on said band,

and said band is superimposed over the selected scale of said cylindrical drum.

12. An analogue measuring machine, as in' claim 1, in which said sensing means includes a lever, a resistance mechanism, a pivot supporting said lever at one end for swinging movement against said resistance mechanism, a segmental rack'having its center of curvature coincident with the pivotal axis of said lever, said lever remote from said pivot being connected to drive said segmental rack, and a gear fast with the first pulley wheel and meshing with the said rack.

13. An indication mechanism, as in claim 4, in which 'a second index is connected to said second band for 

1. An indication mechanism, for moving an index relatively to a scale with parallel calibrations responsive to the sensing means of an analogue measuring machine, comprising first and second pulley wheels substantially frictionless bearings supporting said first and second pulley wheels for rotation about parallely spaced axes of rotation, a thin flexible band has its ends respectively secured to said first and second pulley wheels, a portion of said band positioned between said first and second pulley wheels and connected to the index to move said index relatively to said scale, said first pulley wheel being driven by said sensing means of the analogue measuring machine to move said band and thereby to move said index relatively to said scale, driving means for driving said second pulley wheel to maintain the length of said portion of the band constant, and said band in one position being wound at least one full turn on one of said pulley wheels.
 2. An indication mechanism, as in claim 1, in which said thin flexible band is in the form of a constant force spring tape preset throughout its operative length to the same curvature, said band thereby constituting said driving means whereby the unwinding of said band from either of said pulley wheels will cause a corresponding rotation of the other of said pulley wheels to maintain the length of said portion of the band constant.
 3. An indication mechanism, as in claim 1, in which said driving means is a mechanism including third and fourth pulley wheels and substantially frictionless bearings supporting said third and fourth pulley wheels for rotation respectively about the said axes of rotation of the said first and second pulley wheels, a second thin flexible band has its ends respectively secured to said third and fourth pulley wheels, said third and fourth pulley wheels are connected respectively to said first and second pulley wheels for joint rotation, said second band being arranged whereby rotation of said first pulley wheel in the sense to unwind said first band will cause an equivalent length of said second band to be wound onto said third pulley wheel thereby to cause said fourth pulley wheel to drive said second pulley wheel in the sense to wind up a length of said first band equal to the length unwound from said first pulley wheel, the length of said second band and the number of windings of said second band about said third and fourth pulley wheels being adequate to permit full movement of the index over the scale.
 4. An indication mechanism, as in claim 3, in which said first band is wound around said first and second pulley wheels in opposite senses taken from the ends of said first band.
 5. An indication mechanism, as in claim 3, in which said first band is wound around said first and second pulley wheels in the same sense taken from the ends of said first band whereby the strain energy applied by said first band to said first pulley wheel in any position of said mechanism is substantially equal to the strain energy applied by said second band to said fourth pulley wheel in the same position of said mechanism, and the strain energy applied by said first band to said second pulley wheel in any position of said mechanism is substantially equal to the strain energy applied by said second band to said third pulley wheel in the same position of said mechanism.
 6. An indication mechanism, as in claim 3 in which a second index is connected to said second band for movement along a second scale arranged parallely adjacent the portion of said second band extending between said third and fourth pulley wheels.
 7. An indication mechanism, as in claim 3, in which said first band is wound around said first and second pulley wheels in the same sense taken from the ends of said first band wHereby the strain energy applied by said first band to said first pulley wheel in any position of said mechanism is substantially equal to the strain energy applied by said second band to said fourth pulley wheel in the same position of said mechanism and the strain energy applied by said first band to said second pulley wheel in any position of said mechanism is substantially equal to the strain energy applied by said second band to said third pulley wheel in the same position of the mechanism, a second index is connected to said second band for movement along a second scale arranged parallely adjacent the portion of said second band extending between said third and fourth pulley wheels, and at least one additional pulley wheel is positioned to engage one of said bands to hold said one band substantially parallel to the other of said bands.
 8. An indication mechanism, as in claim 1, in which said driving means is a mechanism driven by said sensing means of the analogue measuring machine and said mechanism is connected to drive said second pulley wheel in unison with the first pulley wheel to maintain the tension in said band whilst it is being unwound from said first pulley wheel.
 9. An indication mechanism, as in claim 1, in which at least one end of said band is secured to its aforesaid corresponding pulley wheel by means of a fixing device positioned within the periphery of said corresponding pulley wheel, said corresponding pulley wheel defining a curved passage having a smoothly curved juncture with the cylindrical operative surface of the pulley wheel, and said band being led to said fixing device through said curved passage.
 10. An indication mechanism, as in claim 1, in which a member having a cylindrical outer surface is mounted for rotation about its axis which is parallely spaced from said portion of said band extending between said first and second pulley wheels, and said cylindrical member defines said scale and a number of other scales which can be moved optionally into operative position adjacent said index by rotating said cylindrical drum.
 11. An indication mechanism, as in claim 10, in which said band is formed at least partly of translucent material, said index is an opaque mark on said band, and said band is superimposed over the selected scale of said cylindrical drum.
 12. An analogue measuring machine, as in claim 1, in which said sensing means includes a lever, a resistance mechanism, a pivot supporting said lever at one end for swinging movement against said resistance mechanism, a segmental rack having its center of curvature coincident with the pivotal axis of said lever, said lever remote from said pivot being connected to drive said segmental rack, and a gear fast with the first pulley wheel and meshing with the said rack.
 13. An indication mechanism, as in claim 4, in which a second index is connected to said second band for movement along a scale arranged parallely adjacent the portion of said second band extending between said third and fourth pulley wheels.
 14. An indication mechanism, as in claim 5, in which a second index is connected to said second band for movement along a scale arranged parallely adjacent the portion of said second band extending between said third and fourth pulley wheels. 